1. Field of the Invention
This invention relates to a method of forming dielectric isolation regions and which is applicable to fabrication of substantially all semiconductor devices such as MOS devices, bipolar devices and the like.
2. Description of the Prior Art
For the formation of dielectric isolation regions, there is known a method in which single crystal silicon is selectively epitaxially grown. This method is described with reference to FIG. 1. First, a silicon oxide film 602 is formed on a silicon substrate 601 by thermal oxidation or CVD, on which is further formed a photoresist pattern 603 serving as an isolation region (FIG. 1(A)). Subsequently, the silicon oxide film 602 is etched substantially vertically by a reactive ion etching technique (hereinafter referred to simply as RIE method) through the photoresist pattern 603 as a mask to form an opening 604 for use as an element region (FIG. 1(B)). Next, single crystal silicon is selectively epitaxially grown on the exposed portion of the silicon substrate 601 by a selective epitaxial growth technique, thereby completely filling the opening 604 (FIG. 1(C)).
The above selective epitaxial growth method has recently attracted attention because fine isolation regions can be formed. For instance, this method has been reported in The Solid State Technology, Japanese Edition, October, 1985, PP. 43-67, under the title of "Improved Dielectric Isolation Method Using Selective Epitaxial Growth".
The selective epitaxial growth method is a simpler process than the trench separation method in which a groove is formed in a silicon substrate and is utilized as an isolation region. However, the selective epitaxial growth method involves the disadvantage that the width of the isolation region is regulated with the processing accuracy of a photoetching technique, so that formation of a finer isolation region is difficult.